A mobile terminal is widely used as a real-time communication tool, and in order to satisfy various scenarios and usage requirements of various user groups, each operator develops a wide range of services, which in common use the network of an operator and service of an operator and require charging. For example in the cases such as business trip or travel, partners that travel together need to communication with each other, but the telephone charge seems higher if a cell phone is used directly for a call. In the same office building, there is no directly connected extension telephone in different companies, so a fixed-line or a cell phone is used for communication which requires charging. Moreover, in the places where there's poor signal or even no signal such as mountain area or outskirts, the cell phone and the like can not implement the function of real-time communication.